The doctor will ask about your symptoms, and medical and family history. A physical exam will be done. There are 4 main tests used to diagnose diabetes. Most tests results should be confirmed with repeat testing. The American Diabetes Association (ADA) recommends using one of the following tests to make the diagnosis:

Random Plasma Glucose Test

Symptoms typical of diabetes include excessive thirst and hunger, frequent urination, and weight loss. Your doctor will make the diagnosis based on your symptoms and the results of the random plasma glucose test. This test is taken any time of day (without regard to when you have last eaten). A sample of your blood will be taken. The blood glucose level will be measured. A measure of 200 milligrams per deciliter (mg/dL) (11.1 millimoles per liter of blood [mmol/L]) or higher along with typical symptoms indicates the presence of diabetes.

Fasting Plasma Glucose Test

You will need to avoid eating for at least 8 hours before the test. A sample of your blood will be taken. The blood glucose level will be measured. A level of 126 mg/dL (7 mmol/L) or higher indicates a diagnosis of diabetes.

Two-hour Glucose Tolerance Test

This starts with a 3-day intake of a diet consisting of at least 150 grams of carbohydrates. You will then be asked to fast overnight (between 8-16 hours). The test is generally done in the morning, in your doctor's office.

A blood sample will be obtained from you to measure the blood sugar level. Then, you will drink 75 grams of glucose dissolved in water. Two hours later, another blood sample will be obtained to measure the blood sugar level. If you have diabetes, your blood sugar level will rise higher than normal and remain high for a much longer time than is normal. A measure of 200 mg/dL (11.1 mmol/L) or higher at 2 hours is considered a positive test.

Hemoglobin A1c (HbA1c)

The HbA1c test is a good indicator of your average blood sugar levels over the previous 2-4 months. This test usually does not require any dietary restrictions. A blood sample will be taken. In most people, an HbA1c level of 6.5% or higher indicates a diagnosis of diabetes.

Other Commonly Ordered Tests

After the diagnosis of diabetes is confirmed, your doctor will most likely order the following tests:

Revision Information

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

Diagnosis of diabetes and prediabetes. National Institute of Diabetes and Digestive and Kidney Diseases website. Available at:
https://www.niddk.nih.gov/health-information/diabetes/diagnosis-diabetes-prediabetes. Accessed August 22, 2016.